| High repetition frequency and narrow pulse width three-wavelength laser is the core detection light source of lidar system,which is widely used in atmospheric detection,ocean detection,land detection,laser ranging and many other fields.This project uses LD end-face pulse pumping Nd:YAG,combined with electro-optic Q-switching technology to obtain high repetition frequency narrow pulse width fundamental frequency optical output,and obtains three-wavelength laser beam splitting output through extra-cavity frequency doubling and sum frequency methods.By optimizing the laser's three-wavelength output single pulse energy and pulse width and other parameters,a laser with high efficiency,compact structure and flexible wavelength switching has been designed and developed.The design and development of the laser has played an important role in promoting the practicality and localization of the laser.In this paper,theoretical simulation and experimental research are carried out around LD pumped high repetition frequency narrow pulse width three-wavelength laser.The main work is summarized as follows:First of all,this article takes LD pumped all-solid-state lasers and nonlinear frequency conversion technology as the research background,and introduces in detail the development history and research status of high-repetition frequency lasers and all-solid-state ultraviolet lasers at home and abroad,and analyzes that the laser design adopts electro-optic Q-switching method combined with extra-cavity frequency doubling and sum frequency conversion technology to achieve high repetition frequency and narrow pulse width three-wavelength laser output.Secondly,compare the advantages and disadvantages of different pumping methods and the characteristics of commonly used gain media,select the end-face pulse pumping method according to this laser design index,determine Nd:YAG as the laser gain media,and design a wide temperature adaptable laser.Study the thermal lens effect of laser crystals and design a stable resonant cavity.Establish electro-optic Q-switching rate equations and simulate the laser dynamics process.Perform theoretical simulation on the best transmittance of the output mirror.Then,select both the frequency doubling crystal and the sum frequency crystal to be LBO,and carry out the simulation calculation of the phase matching angle,and carry out the phase matching design.Study the influence of the peak power density of the injected laser,the length of the nonlinear crystal,the amount of phase mismatch and other factors on the nonlinear conversion efficiency and perform simulation analysis.The study of the effect of frequency-doubling conversion efficiency on the sum-frequency conversion efficiency points out the optimization direction for realizing that the laser three-wavelength single pulse energy meets the design indicators.Finally,based on the above theoretical analysis and numerical simulation calculations,the experimental research of LD pumped high repetition frequency narrow pulse width three-wavelength laser is carried out.The LD end face pulse pumps Nd:YAG,the electro-optical switch is KD*P,the transmission rate of the output mirror is 70%,the flat and flat cavity has a compact structure,and the cavity length is 145mm.Out-of-cavity frequency doubling and sum frequency,frequency doubling crystal and sum frequency crystal are all LBO crystals.Three dichroic mirrors are used to split the output of the three-wavelength laser.The laser can switch wavelengths flexibly.Under the conditions of pumping 24W and repetition frequency of 1kHz,the single pulse energy of three-wavelength laser is1.18m J@1064nm,1.06m J@532nm,0.73m J@355nm;the pulse width is 3.83ns@1064nm,3.42ns@532nm,3.02.ns@355nm;beam quality factors are M_x~2=1.703,M_y~2=1.750@1064nm,M_x~2=1.506,M_y~2=1.365@532nm,M_x~2=1.514,M_y~2=1.389@355nm;the short-term instability of 1064nm output power is 0.39%,the short-term instability of 532nm output power is 1.21%,and the short-term instability of 355nm output power is 1.62%. |
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